Abstract: In order to address the tough issue of‘strong-ductility trade-off’ for the structural application of high entropy alloy (HEA), a FeMnCoCr high entropy alloy with heterogeneous grain size was prepared by the combination of cold rolling and heat treatment, and the effects of different annealing temperature and time on its microstructure and mechanical properties were studied. The results showed that the increase of annealing temperature could promote the nucleation and growth of dynamically recrystallized grains, and enhanced the difference in grain size between coarse and ultrafine grains, as well as the proportion of coarse grains. Additionally, an annealing temperature of 730 ℃ contributed to the best comprehensive strength and plasticity combination of micro-hardness 213 HV, yield strength 705 MPa, tensile strength 910 MPa and fracture elongation 42.5%. The product of strength and tensile elongation reached approximately at the high value of 35.9%.